#https://www.luogu.com.cn/problem/P2437


From,To =readline.split(' ').map(&:to_i)
Delta =To - From

def res(x)
	@cache ||={};
	if ! @cache.has_key?(x)
		if x<=2 
			@cache[x]= x
		else
			@cache[x]= res(x-1)+res(x-2)
		end
	end
	@cache[x]
end

Res = res(Delta)
puts Res
